1. Field of the Invention
This invention relates to a compact induced current heat-generating pipe and a construction wherein the same is applied.
2. Description of the Prior Art
Heretofore, a heat-generating pipe referred to as induced skin effect current heat-generating pipe has been known and applied to heating of pipelines, etc. This heat-generating pipe is described in e.g. "Electric Engineering Handbook" edited by The Institute of Electrical Engineers of Japan, page 1578, 1978 edition, and the specification of Japanese patent publication No. Sho 46-588 (1971) (to which U.S. Pat. No. 3,515,837 corresponds). This heat-generating pipe is composed of (1) insulated wires either in two rows in the case where an electric source of single-phase alternating current is employed, or in the three rows in case where an electric source of three-phase alternating current is employed, the respective ends of these wires on one side being electrically connected to each other and those on the other side being connected to the respective phases of the above-mentioned alternating current electric source, and (2) two or three electrically conductive ferromagnetic pipes through which the respective wires in such rows are passed, and which are electrically connected to each other at both the ends thereof; the thickness of the ferromagnetic pipe being made at least twice the skin depth of the alternating current to be passed through the pipe; and when the alternating current flows through the ferromagnetic pipe, it is concentrated on the inner skin portion of the pipe and heat is mainly generated there.
However, the electrically conductive ferromagnetic pipe of the above-mentioned induced skin effect current heat-generating pipe is required to have a thickness of at least twice the skin depth of the alternating current as mentioned above so that the alternating current flowing therethrough substantially does not appear on the outer surface of the pipe; hence such a heat-generating pipe is restricted in the uses.
For example, if a commercial frequency of 50 Hz or 60 Hz is employed for the alternating current source and a commercially available steel pipe is employed as the above-mentioned electrically conductive ferromagnetic pipe, the above-mentioned skin depth is about 1 mm; hence a steel pipe having a thickness of about 3 mm and an inner diameter of about 15 to 50 mm should be employed. Such a heat-generating steel pipe is suitable to heating and temperature-maintenance of pipelines having a length of several kilometers or longer and an inner diameter of 10 cm or more, but when such a pipe is applied to small scale pipelines having e.g. a length of 1 Km or less, particularly several tens to several hundreds meters and a diameter of 5 cm or less, such a pipe is too large, resulting in the following inconveniences:
(1) In the case of the above-mentioned dimensions of the heat-generating steel pipe, i.e. a thickness of 3 mm, and an inner diameter of 15 to 50 mm, such pipe has a large geometrical moment of inertia and a low flexibility; hence its contact with transporting main pipes which is necessary for heat transfer from the pipe to the main pipes is difficult. Thus, welding or the like means has heretofore been applied. However, welding not only requires a special technique, but cannot be applied at the site where flammable gases are liable to be generated. Further, it is also uneconomical to employ welders for small scale pipelines.
(2) When the heat-generating steel pipe has a large diameter as compared with that of transporting main pipes, a covering heat-insulating cylinder having a larger diameter is required as compared with the case where other kinds of heat-generating bodies having a smaller diameter are employed, which is uneconomical.
Such inconveniences can be overcome by reducing the outer diameter and thickness of the heat-generating pipe. Namely, the flexibility of the heat-generating steel pipe increases in inverse proportion to its geometrical moment of inertia, which, in turn, is proportional to the difference between the fourth power of the outer diameter of the pipe and the fourth power of the inner diameter thereof, and as a result, approximately proportional to the product of the third power of the average diameter by the thickness; hence the moment can be reduced by reducing the inner and outer diameters and also reducing the thickness.
The inner diameter of the heat-generating steel pipe is restricted in the minimum value by the diameter of the insulating wire passed through the inside of the pipes. On the other hand, as to the thickness of the heat-generating steel pipe, if the thickness t is decreased so as to give a relationship EQU t&lt;2s
wherein s represents the so-called skin depth showing a range within which the alternating current flows through the pipe, then there may occur a danger that an alternating voltage appears on the outer surface of the heat-generating steel pipe.
Contrary to the case of the above-mentioned induced skin-effect current heat-generating pipe, the first object of the present invention is to make the thickness of the electrically conductive ferromagnetic pipe less than twice the skin depth of the alternating current flowing through the ferromagnetic pipe, and also suppress the voltage appearing on the outer surface of the pipe to substantially zero or to an extent not harming safety.
The second object of the present invention is to provide a compact and small scale heating apparatus which is convenient for heating.
The third object of the present invention is to provide a construction wherein heat can be well transferred without welding, in the case where it is impossible or undesirable due to the material, environment, small scale, etc. of the body to be heated, to weld the heat-generating pipe onto the body to be heated.